1. Field of the Invention
This invention relates to a resin or plastic molded (or encapsulated) type semiconductor device.
2. Description of the Related Art
FIG. 11 is a front view of a conventional resin molded type semiconductor device. FIG. 12 is a sectional view of the conventional resin molded type semiconductor device. In this figure, it is also illustrated how a screw for mounting the device is inserted thereinto. As shown in FIG. 11, the conventional resin molded type semiconductor device is provided with an electrode lead 6 serving as a first external electrode. Further, a semiconductor element 3 is fixed onto a rectangular heat sink 1, including a mounting hole 10 by solder 4. Thereby, the semiconductor element 3 and the electrode lead 6 are connected to each other electrically and thermally. Further, the semiconductor element 3 and another electrode lead 7 serving as a second external electrode are connected to each other by a bonding wire 5 acting as a conducting means and are thus connected to each other electrically. The electrode lead 7 is composed of an internal electrode 7a, which is a part to be molded or sealed with resin, and an external electrode 7b which is a part to be exposed to the outside or exterior. The heat sink 1, the semiconductor element 3 and the internal electrode 7a are sealed with a sealing or encapsulating resin 2.
In the case of the resin molded type semiconductor device having such a configuration, the solder 4 is used when the semiconductor element 3 is securely fixed to the heat sink 1. The solder 4 sandwiched between the semiconductor element 3 and the heat sink 1, however, should be of uniform thickness. Therefore, when the semiconductor element 3 is firmly fixed to the heat sink 1 after the solder 4 is applied, it is necessary to perform scrubbing which is an operation of shaking the semiconductor element 3 on the heat sink 1 to make the solder 4 even and enhance the conformability of the solder 4.
Preferably, the semiconductor element 3, which acts as a heat generating element, is accurately positioned at a predetermined distance from the mounting hole 10 in such a manner that the semiconductor element 3 is not crushed on the heat sink 1, to which the element 3 is fixed, by the head of the screw 11 used for mounting the heat sink 1 to an external chassis, with the intention of permitting the generated heat to escape to the exterior. Further, multi-pin (or high-pin-count) semiconductor elements or devices developed in recent years require high-accuracy wire bonding. Moreover, it is desirable for achieving a high-accuracy wire bonding that the semiconductor element 3 be accurately positioned at a predetermined mounting location on the heat sink 1.
As described hereinabove, it is required that the semiconductor element 3 be accurately positioned on the heat sink 1. To that end, there has been devised a method by which a projection for positioning is provided on the heat sink 1 and thus the semiconductor element 3 is accurately fixed to a predetermined position on the heat sink 1 (see the Japanese Utility Model Public Disclosure No. 4-10346/1992 Official Gazette).
FIG. 13 is a front view of an example of the semiconductor device disclosed in the Japanese Utility Model Public Disclosure No. 4-10346/1992 Official Gazette. FIG. 14 is a sectional view of the example of the semiconductor device of FIG. 13. As illustrated in FIG. 13, in the case of this device, continuous frame-like walls 9a, 9b, 9c and 9d are provided in such a way as to surround four sides of the semiconductor element 3. Thereby, the semiconductor element 3 is positioned at a predetermined location and is further fixed thereat.
However, in the case of the aforementioned conventional positioning method, the semiconductor element is completely fixed onto the heat sink 1. It is, therefore, impossible to scrub the semiconductor element 3.
Thus, although the semiconductor element 3 can be accurately positioned at the predetermined mounting location on the heat sink 1, the thickness of the solder 4 between the semiconductor element 3 and the heat sink 1 can not be made to be uniform. Further, because the solder 4 is surrounded by the continuous walls, there is no escape path for the solder 4 when the semiconductor element 3 is pressed or scrubbed.
The present invention is accomplished to solve the aforementioned problems of the conventional device and method.